1. To use rat monoclonal antibodies to the rat "I-A(u)" and "I-E(u)" class II major histocompatibility complex antigens to prevent insulin dependent diabetes mellitus (IDDM) in the BB/Worcester rat. 2. To produce rat monoclonal antibodies to the rat islet cell surface antigen(s) (ICSA) expressed on insulin producing Beta cells. 3. To use monoclonal Alpha-ICSA antibodies to isolate and characterize rat ICSA. 4. To use affinity purified ICSA to prevent IDDM in the BB/Worcester rat. 5. To use purified ICSA to develop a rapid assay for Alpha-ICSA antibody. 6. To clone and sequence the cDNA sequences encoding the variant sub-types of HLA-DR4Beta, HLA-DR3Beta, HLA"DC4"Beta, and HLA-"DC3"Beta.